In a number of industries, bores are drilled from surface in order to access subsurface formations, including for example hydrocarbon-bearing or geothermal formations. One method of forming a bore comprises drilling to a first depth and running a first tubular section or string of tubular sections, known as casing, into the bore. The casing is suspended from surface and the annulus between the exterior of the casing and the surrounding bore wall is filled and sealed with cement. The bore is extended and a further tubular section or string of tubular sections, known as liners, are run into the bore and suspended from the casing and the annulus between the exterior of the liner and the surrounding bore wall is also filled and sealed with cement. In order to access the formation, the liner and cement are perforated to provide a fluid flow path between the formation and the surface.
Traditional methods of forming a bore can be both time-consuming and costly. Furthermore, it is common for the tubular string, during run in, to encounter obstructions in the bore, for example, beds of drill cuttings lying on the low side of an inclined bore, ledges, bore discontinuities, set cement or the like which can obstruct location or progress of the tubular string or other bore tools, thereby inhibiting or complicating formation and operation of the bore.
In order to improve the surface texture and geometric tolerances of the bore, the leading end of the tubular string may be provided with a shoe having blades arranged around its exterior surface. The blades are adapted to engage the interior of the bore and, typically, the tubular string is rotated or reciprocated to remove material from the bore wall or clear obstacles in the bore by a reaming process. In some applications, a portion of the shoe may be tapered off bore-centre to provide a nose portion.